Researches On Axial Compressive Stress-Strain Relationship Of Concrete Confined By FRP

The technology of CFRP (Carbon Fiber Reinforced Plastic) and GFRP (Glass Fiber Reinforced Plastic)confining concrete structure has been rapidly developed at home and abroad, it has received significant attentions in civil engineering due to their unique properties, such as high strength-to-weight radio, good resistance to corrosion and fatigue, convenient to construction and no additional dimension. However, most information available in our country is on the study of FRP confining concrete cylinder properties, little information on the properties of FRP confining concrete prism is available.The improved robust design method is applied to analyze several important factors of concrete by FRP.the purpose is used base in following test and design.Study the properties of FRP confining concrete column through sixteen groups columns subjected to axial loading, and receive the stress-strain curves; various design parameters, such as amounts of FRP sheets, width of straps and spacing of straps, have been considered. The results are:The axial compressive strength and ductility of concrete prism wrapped by CFRP sheets or CFRP straps have all increased to a certain degree, the process of destruction of concrete prism wrapped by CFRP become slower than common concrete prism. For fully wrapped concrete prism, the axial compressive strength increased 15.1%,35.3%,58.3%, respectively. For separately wrapped concrete prism, the largest increased axial compressive strength is the specimen wrapped by the width of 60 millimeters CRFP straps, is 13.6%. The results are:The axial compressive strength and ductility of concrete prism wrapped by GFRP sheets or GFRP straps have all increased to a certain degree, the process of destruction of concrete prism wrapped by GFRP become slower than common concrete prism. For fully wrapped concrete prism, the axial compressive strength increased 14.3%, 25.0%,25.9%, respectively. For separately wrapped concrete prism, the largest increased axial compressive strength is the specimen wrapped by the width of 40 millimeters GRFP straps, is 14.6%.Based on the test results, deducing and validating the stress-strain relationship model of FRP confined concrete. The results are:For concrete prism wrapped by FRP sheets, after the stress exceeds the peak stress, the stress may ascend slowly with adequate confinement, or it may be almost unchanged with moderate confinement, or it may descend slowly with deficient confinement. The experimental stress-strain diagram has three different stages. Firstly, the initial portion of the stress-strain response of confined concrete follows the path of unconfined concrete. Secondly, after exceeding the unconfined strengthen of concrete, the curve starts to form a transition zone. Finally, the FRP sheets are fully activated and the confining stress provided by the FRP sheets continues to increase with the applied load until failure.Because the temperature-swelling coefficient is different between FRP and concrete, temperature stress is produced when the temperature changes. The temperature stress is emulated by the ANSYS finite element program under the difference temperature of 30℃, 40℃,50℃,60℃. As the difference temperature increases, the temperature stresses increase. Under the difference temperature of 60℃, the largest temperature stress is 184Mpa, the largest compressive stress in CFRP sheets is-211Mpa.Through date to make cost-effectiveness compare GFRP and CFRP, exposition the application of GFRP practical significance and economic applicability on our country in the morden, no special requirements on confining concrete structure, GFRP should be given priority.